July 27 - August 2, 2000 7 CLEO - classe
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Transcript July 27 - August 2, 2000 7 CLEO - classe
*
c
First Observation of the Baryon;
0
0
Properties of c , c , c , and c Baryons
Andreas Warburton
Cornell University
CLEO Collaboration
XXXth International Conference on High Energy Physics
ICHEP 2000, Osaka, Japan
July 27 August 2, 2000
PA01c50
Talk Overview
CLEO
All new results are preliminary!
Charmed-Baryon Spectroscopy
CLEO Charmed-Baryon Reconstruction Techniques
Mass and Width Measurements of the
Discovery of
*
and
Mass
Measurement
of
the
c Baryon
c
First CLEO Observation of the
July 27 August 2,
0c and c Baryons
ICHEP 2000
0c Baryon
A. Warburton
Cornell University
2
CLEO
The Charmed Baryons
Charmed baryons consist of a heavy c
quark and a light diquark
Many JP states
To date, all L=0 states seen except
*c and 0
c
diquark
antisymmetric
under SU(3)
None of the JP quantum numbers has
been measured!
July 27 August 2,
ICHEP 2000
A. Warburton
diquark
symmetric
under SU(3)
Cornell University
3
c and c Spectroscopy
CLEO
#
#
Not yet
observed
#
#
#
July 27 August 2,
ICHEP 2000
A. Warburton
#
Cornell University
4
Data Set and CLEO II/II.V Detector
CLEO
e+e Collisions near (4 S )
Resonance (~10.5 GeV)
Ldt
14 fb 1
Charm-quark Production:
B-meson decays
e+e cc jets
Two Configurations:
CLEO II (1989 1995)
CLEO II.V (1996 1999)
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
5
Reconstructed Candidate Modes
CLEO
0
and
c
and
c
0
c
c c
* 0
c
c
0
0 K
c
15
modes
Hyperon Channels
Mode found by E-687
0c K K
K
July 27 August 2,
ICHEP 2000
A. Warburton
p 0
p
Cornell University
6
CLEO
Event Selection and Background Suppression
Principles
candidates are reconstructed in the CsI calorimeter barrel
0
region
p, K , candidates are identified using time-of-flight and dE/dx
info
Displaced vertices are used to identify , , , ,
candidates
Scaled Momentum criterion: xp > 0.5 or 0.6, where xp p/pmax
and pmax Ebeam Mcand.
reduces combinatorial background
Note: charmed baryons with B-meson parents have xp < 0.4
2
July 27 August 2,
ICHEP 2000
A. Warburton
2
Cornell University
7
CLEO
15 c Modes
• xp > 0.5
• Signal region: 1.6
• Yield ~ 58 000 candidates
• S:N ~ 1 : 1.2
Mass – M
c
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
8
K
26723 207
742 34
p
CLEO
Inclusive
Hyperon
Samples
July 27 August 2,
18606 527
ICHEP 2000
69484 731
A. Warburton
Cornell University
9
CLEO
c
Resolution
Function
c
and 0c Mass
and Width Fits
• Double-Gaussian resolution
function ( ~ 0.6 MeV/c2)
• Yields: ~ 2000 events
0c
Resolution
Function
• Fit to p-wave Breit-Wigner
convolved with resolution
function
• xp > 0.5
July 27 August 2,
M c+ M c+
ICHEP 2000
A. Warburton
GeV c 2
Cornell University
10
CLEO
c
and
c
661
Yields
c
63
60
Events
c
327
78
73
MeV c 2
Events
• Mass Fits to p-wave
Breit-Wigner convolved
with resolution function
• xp > 0.6
• First observation of
resonance
c
M c+ 0 M c+
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
11
CLEO c Mass and Width Measurements
CLEO
c0
Observable Isospin
M
M c c
P
1
J 2
c
J
P
3
2
c
c
c
c
c
167.2 0.1 0.2 166.4 0.2 0.3 167.4 0.1 0.2
2.4 0.2 0.4
4.6 (90% CL)
2.5 0.2 0.4
232.6 1.0 0.8 231.0 1.1 2.0 234.5 1.1 0.8
13.0
3.7
3.0
4.0
17 (90% CL)
17.9
+3.8
3.2
4.0
PRELIMINARY CLEO results
G. Brandenburg et al. (CLEO), Phys. Rev. Lett. 78, 2304 (1997)
All quantities are in MeV c 2.
First uncertainties are statistical; second are systematic.
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
12
0
0K
K
K K
CLEO
0c Search Modes
xp > 0.5 or 0.6
Invariant Mass GeV c 2
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
13
CLEO
Wrong-Sign Daughter Combinations
Hyperon-Sideband Distributions
Sum of 5 0c
Search Modes
Total Fitted Yield:
40.4 9.0 (stat.)
candidates
0c Candidate Mass GeV c 2
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
14
Summary of Preliminary Results
0
c
CLEO
Mode
0
Fitted Yield
13.3 4.1
11.8 4.9
Relative B
1.0
4.2 2.2 1.2
B ffb
11.3 3.9 2.3
47.6 18.0 2.8
0.9 1.4
0.6 90% CL
5.1 90% CL
0 K
K
9.2 4.9
7.0 3.7
4.0 2.5 0.6
1.6 1.1 0.4
45.1 23.2 4.1
18.2 10.6 3.8
Combined
40.4 9.0
K K
9.5 90% CL 4.8 90% CL 53.8 90% CL
Unbinned maximum likelihood fit mass:
M 0c 2694.6 2.6 stat. 2.4 syst. MeV c 2
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
15
Conclusions
CLEO
We
present the most statistically accurate
0
measurements of the c , c , and c masses.
We have made
c widths.
preliminary measurements of the c and
0
We
report the first observation of the
measure its mass to be
c baryon and
2
M
231.0
1.
1
sta
t.
2.
0
syst.
M
eV
c
c
c
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
16
Conclusions, cont’d
CLEO
CLEO
has now, for the first time, observed a significant
0
number of c candidates. We present a preliminary
mass measurement of
M 0c 2694.6 2.6 stat. 2.4 syst. MeV c 2
Supporting
documentation can be found in
hep-ex/0007041
hep-ex/00070
CLEO
continues to contribute to knowledge of the
charmed baryon sector.
July 27 August 2,
ICHEP 2000
A. Warburton
Cornell University
17